My stack of rejects is getting higher!

General Composites Discussions Composites Talk
#1

I know I’m doing something wrong, but I don’t know what it is exactly. :frowning: I’m getting voids, but I don’t know why. I’m getting bummed. So, I’m humbly asking for some ideas.

My molds are simple boxes with rounded corners. My stack consists of two layers of 668gsm CF twill around SF3 Soric. I’ve been using Adtech EL-360 and 820 epoxy. I pull a vacuum, (~29.25inHg at my altitude), for at least 1-1/2 hrs, (2 or more if it’s humid). I insure there are no leaks. I infuse at bottom, center, vacuum around the perimeter. I degas. I throttle my resin flow. I use a hemostat at the very end of the resin tube. There are no air that enters, yet I get bubbles!

I have the following practices that I wonder about:

[ol]
[li]I’m somehow not degassing properly.
[/li]
[li]I’m not pushing my corners down well enough, (or early enough) when initially collapsing the bag.
[/li]
[li]I don’t use mesh under the the vacuum spiral.
[/li]
[li]When I’m done, I just clamp everything off, and shut things down.
[/li][/ol]

I thought I knew how to degas… Yet, my resin bubbles after the initial boil off, for more than 15min. Am I being too impatient? I put in a piece of Scotchbrite in the mix.

I don’t believe I have a bridging problem, but sometimes when I look at my corners the radius looks too round. That said, the corners which I feel are good, have bubbles just the same. Maybe I need glasses??

At some point I stopped putting peel ply and mesh under the vacuum hose. (I think when I experimented by not using any mesh at all, and just used the flow properties of Soric alone, I stopped using it.) BTW, those were some of my best parts. Unfortunately, this practice is incompatible with temperatures below 85 degrees F. I now use peel ply and mesh only on the bottom, and I simply lay my spiral on the reinforcement stack on the flange.

At times it’s hard to know what’s solid advice and what’s done for product marketing or hogwash. One such topic is when are you done? When I’m done infusing, I clamp it, and shut things down. I’ve read from some people that they keep the vacuum up until the part is cured. Others say: When it’s done it’s done. I’ve also read a mixture of the two positions. Pulling a vacuum until it’s cured, (24hrs), seems wasteful to me, (after 6 or so hrs, 15psi isn’t going to move resin that viscus!)

That’s all I can think of. Let me know what else I can relate. I need to fix my flawed practices!

#2

  1. It is hard to tell from the picture but I would say that a bubble that large is not the result of not degassing properly. It may be an area that closed out and did not fill with resin, are you sure the Soric is continous through this area? Is your vacuum line continuous around the perimeter?

  2. Even if you did have some bridging in this area I would expect it to just fill up with resin. I usually pull a light vacuum and position the bag, increase vacuum and resposition the bag and so on to eliminate bridging.

  3. I dont see this as a problem.

  4. I would keep the part under vacuum at least until the resin gels, I see no downside to leaving the part under vacuum as it cures. You can clamp off the feed line(s) and the line between the vacuum pump and catch pot/vacuum reservoir and you should hold vacuum for a long time assuming you have no leaks.

You may want to try adding flow mesh in the corners to improve flow in those areas.

#3

You had a leak, there is no reason to leave your pump on until your part gels or cures, that why you do a good leak test prior to infusing.

#4

Thanks for your input. :smiley:

Yes, they’re large bubbles! Almost always in the corners. --But, I’ve been making a concerted effort to cut my Soric so there are no gaps. It also appears in simple two surface corners. (i.e. Where bottom and side meet) Perhaps I should use mesh up past the corners???

Your assessment of Item 2 seems logical. The larger bridges I’ve experienced in the past, (long ago, when I believed bagging plastic could actually stretch as far as they show! :wacko: ), it simply welled up in the corners. (Then I discovered pleats! :smiley: I now have ample un-stretched bag.) So, I made it a point to push down the corners, but haven’t thought much about it lately. This time I had “help”, and I had to re-adjust things after they said it was all down, which is kind of too late. BTW, I’ve been doing two castings at one sitting, sharing common plumbing. I do them sequentially, but the problem was happening before this.

I understood a break in the mesh will cause a “break”, for purposes of slowing things down and for eliminating bubbles as I recall. That said, my break is ~6" on one mold, and it really makes things slow way down. So much so, that my pot nearly goes exo as I get toward the end. (Especially when doing two.)

I’m I right in getting the idea, my fabric is perhaps starved of resin???

#5

From the looks of it, it seems an enclosure, not a leak. Which means your bag is OK, but your strategy is seemingly not.

These are just rectangular boxes, right? It looks like bridging, which needs more resin to fill, but as it fills, the resin runs around it through the permeable soric, and you end up with an enclosure.
Only remedy is to check even better for bridging.

As a workaround you can try clamping off the vacuum side instead of the resin side, and leave the resin side open, with the feed pipe in the pot. Not suitable for weight sensitive products, though. (even with this system it is important to get a “full pull” as to minimise air under the film.)

#6

Herman, you’re very insightful! :smiley:

I think, because we’re:
[ul]
[li]Doing two molds at once.
[/li][li]Have stopped using adhesive and are now,
[/li][li]Wrangling the spiral tubing under vacuum.
[/li][/ul]

We’re not dealing properly with the corners at that critical moment when the fabric needs to be seated. There’s only one shot at truly seating it at the lower initial vacuum. Once you lock it down fully, it’s tough to pull it back up, (through the bag), and reseat it.

I suspect once I get the material seated, I can then go back and fiddle with the spiral hose.

#7

I have no idea of how many you should make, but you could consider laminating a glass product nicely in your mould, finish that, and cast a countermould in that, which can act as a press to force the fiber in position.

#8

Just from the corner bubble, try slowing the infusion down when the flow front gets to the corners. Even clamp it would work. After a few min, you can let the resin flow again. Maybe the resin is flowing too fast, and when it racetracks around the corner, any air gets stuck there. If you have no leaks, then you can let the resin fill that area slowly, making sure all air is drawn out.

#9

Waiting for some supplies… I’ll try some different things and report the outcome. Thanks everyone! :slight_smile:

#10

I have never worked with soric and I am confused. The mfr of Soric claims that Soric does not absorb resin into the cells. How then does the resin make it through your stack if you begin infusing in the center of your part and drawing resin outward? It must allow resin to pass through somehow.

#11

The resin flows through channels between the cells.

#12

So if you were to cut through the cured stack you would run into resin channels and un-saturated cells correct?

#13

Correct.

#14

Many reject areas can probably be cut out with a razor ( or drill a couple tiny holes) and filled or injected with clear resin.

Poly suringes work well for this.

Herman is that Lantor Soric? what size (mm) are those cells?

#15

Yes, Lantor Soric.

The XF version has some 8mm cells (or so, from memory)
The SF version has some 4mm cells

The TF version has random dots

The LRC version has 15mm cells

All sizes approx, I do not have the stuff at home.

#16

My supplier does not carry Soric, but does carry Nidacore. Much difference?

Sorry for the threadjack.

#17

Nidacore is plastic honeycomb, which is totally different.

#18

I am having a hard time understanding the Soric. If it has cells, and the resin passes around them, and you infuse in the center of the stack, the resin must travel through the Soric resin channels to get to the mold surface.

Does it make a difference infusing above the stack and pulling it through to the mold surface vs infusing the stack from one end, allowing the resin to flow on both sides of the Soric, thus pulling the air along with it?

It just seems to me that the cells could trap air below them as the resin makes it’s way through the stack.

#19

You are right about the possibility of air entrapment, however the cells are not solid material, but are an accumulation of microspheres, slightly porous, so if needed, air is drawn from the surface.

Besides that, the cells are so small that entrapment of air is not a concern. I even infused a single layer of biax 450 gr/m2, with LRC Soric, without any problems (I did use a flow mesh on top of the laminate, however)

#20

Thanks, I was thinking the cells were the actual size of the honeycomb and un-impregnable.